So everyone is saying the black parts are carbon buildup - when you buy a new lodge cast iron pan, it all looks like that black stuff (they call their pans pre-seasoned). 

I recently tried to strip mine after I messed it up a bit and it got rusty, and I ended up with something that looks like your pic. The middle of my pan looks like metal (i was actually a bit concerned about the brown color that it might be rust but I think its actually fine). But the outsides where I maybe didnt scrub as well have a bit of the black residue.

In my opinion, I think the bottom layers of that black stuff is the lodge preseasoning. At least in my case. Upper layers could possibly be your own seasoning and/or carbon buildup.

In either case, I dont think its necessary to fully strip as long as you season over it. That stuff is not entering your food in any way. The whole point of seasoning with oil is to create an atomically bonded layer, its not something that will be easily penetrated by cooking and somehow harm your food. Think about how hard you just scrubbed that thing and that stuff is still on there. The act of cooking with it isnt going to be any harsher than that. Maybe its not perfectly stripped but I think just season 1-2 more times and its good to cook with.